1. Field of the Invention
The invention relates to a drive unit composed of a movable part and a stationary part.
2. Description of the Prior Art
In recent years, a demand for a drive unit utilizing linear drive as typified by a linear motor has increased. The linear motor has advantages in capability of high speed and high accuracy positioning and easy maintenance as compared with a rotary motor in the field where the linear drive is needed and thus, has been extremely demanded particularly in the field of a semiconductor manufacturing apparatus, a working machine or the like. However, not limited to the fields, it is also expected that the linear motor will be used in other applications in which the above advantages can be made use of.
There are various systems for the linear motor. For example, JP-A-10-174418 (referred below to as a conventional example 1) describes a linear motor in which a stationary part is composed of a plurality of C-type iron cores having a coil wound therearound, a movable part is composed of a plate-shaped member with a plurality of permanent magnets arranged thereon, and the movable part is disposed in a gap in the stationary part iron core. Further, JP-A-2001-28875 (referred below to as a conventional example 2) describes a linear motor in which only one coil is wound around a stationary part in order to achieve easy manufacturing and space saving and to improve electrical efficiency, and iron cores having two kinds of shapes are alternately arranged in the stationary part.